Tumbling of stones and other objects in a barrel in order to polish them for lapidary purposes is an old and well-known art. That type of tumbling is not very lengthy, often needing literally weeks, but also tends to remove and polish the high spots only with consequent loss of details and dimensions. Vibratory tumbling, on the other hand, not only requires dramatically less time but allows intricate shapes to be smoothed with little loss of material and dimension. This is probably because the material being moved very rapidly in very small increments so that the surface of the material is much more evenly treated. In vibratory tumbling, as opposed to barrel tumbling, it is essential where the abrasive is in a liquid medium that at all times there be a thick coating of abrasive on the stones or objects; if the liquid is too thin so that is cannot cling to the material, the two tend to separate, the abrasive sinking to the bottom and the material remaining on top.
At the same time and for the same reason the mass of material and abrasive must also rotate about a "center" in the container and, in order additionally to increase the abrasive action and further reduce the required time, the mass should be "compacted" as it rotates so that the material does not freely separate as is the case in barrel tumbling. Compacting in turn usually demands that the container be at least 70-75% full, unlike the case of barrel tumbling, because it is the confining aspect of the walls of the container which provides the compaction as the mass rotates. While vibratory tumbling in the foregoing manner has greatly reduced the time necessary to polish stones and other objects -- from 4 to 6 weeks in the case of barrel tumbling to 7 to 10 days in the case of vibratory tumbling using the machine of my prior U.S. Pat. No. 3,197,922 -- yet it obviously would be helpful to reduce the latter time still further. That, therefore, is the primary object of the present invention.